1. Field of the Invention
The present invention relates to an ink-jet recording apparatus for discharging ink from a recording head to a recording material to effect recording and to a control method of the apparatus.
2. Description of the Prior Art
A recording apparatus such as a printer, a copier, a facsimile or the like is constructed to record an image comprising a dot pattern according to image information on the recording material such as paper, cloth, plastic film and the like.
Recording apparatuses can be divided into an ink-jet type, a wire-dot type, a thermal type, a laser beam type and the like according to the recording method; of these, the ink-jet type (ink-jet recording apparatus) is constructed so that an ink (recording liquid) drop is discharged from a discharge port of the recording head to adhere to the recording material thereby achieving recording.
Recently, an increased number of recording apparatuses have been used, and high-speed recording, high resolution, high image quality, and low noise are required for these recording apparatuses. The ink-jet recording apparatus can be one of recording apparatuses which meet such requirements.
To achieve a high-quality printed image, recently various attempts are being made for outputting pictorial images using an ink-jet printer. One of the examples is a recording method which uses a reduced dot diameter of ink droplet. By reducing the dot diameter, a particulate state (coarse feeling due to ink droplets) in a high-contrast portion can be reduced.
However, if the dot diameter of all ink droplets is reduced, an increased number of dots to that extent must be applied, which increases the amount of data and the time required for printing.
For example, FIGS. 29A and 29B show cases of printing with densities of 360 dpi (dots/inch) and 720 dpi in an area of {fraction (1/360)} inch square. When printed with 360 dpi, recording is completed by only one dot in the area; however, when printed with 720 dpi, recording is not completed unless up to four dots are recorded in the area. It can be seen that even when printing in the same area, if the resolution is increased to two times and the dot diameter is reduced, four times the number of dots, that is, four times the amount of data, are required.
The dot diameter of an ink droplet on paper increases with increasing ink amount discharged from the discharge port of the print head. To increase the amount of ink droplet discharged from the discharge port, energy applied for ink discharge is increased, or for the case of a thermal ink-jet printer using an electrical-thermal conversion element (discharge heater), the area of the discharge heater is increased.
For example, when the area of the discharge heater per one nozzle (unless otherwise specifically noted, hereinafter used to collectively refer to the discharge port, a liquid passage communicating with the discharge port and a device to generate energy utilized for discharging) is enlarged, the size of a formed bubble is also increased by the function of thermal energy, the ink amount pushed out by the bubble is increased, and an ink droplet of large dot diameter can be formed. Hereinafter, this is called a large dot. On the contrary, when the area of the discharge heater per one nozzle is decreased, the size of the formed bubble is also decreased, and, as a result, the discharge ink amount is decreased, and an ink droplet of small dot diameter can be formed. Hereinafter, this is called a small dot.
Further, by appropriately determining the shape, size, disposition or number of discharge heaters so that a bubble covering a large area of the discharge heater is formed when printing a large dot, and a bubble covering a small area of the discharge heater is formed when printing a small dot, that is, by varying the area of bubble generation, it is possible to selectively print a large dot and a small dot even with a single nozzle.
As described above, a recording head is developed which is capable of selectively printing large and small dots by controlling application of energy (applied energy) provided for the discharge operation. By using this recording head, high image quality can be achieved with an ink-jet recording apparatus.
Still further, for the ink-jet recording apparatus, since an ink is discharged from the recording head, stabilization of ink discharge and stabilization of ink discharge amount are required in order to meet the above requirements. Stabilization of ink discharge is achieved by the following means.
Specifically, in the ink-jet recording apparatus, a cap for capping the discharge port is provided which is used to make suction recovery operation for eliminating or preventing discharge trouble by sucking the ink from the discharge port of the recording head.
Yet further, there is a case in which in association with the progress of discharge operation, ink splashed back from the printing medium or mist and the like generated during discharging accumulate in the vicinity of the discharge port, and the accumulated ink adheres to the discharge port resulting in discharge trouble such as discharge failure or altered discharge direction. To prevent this, a construction is employed in which ink on the surface is removed by wiping the surface (face) where the discharge port of the recording head is disposed with a wiping member such as urethane rubber or the like. Although the wiping performance of the wiping member depends on the material quality and mechanical setting conditions, to always maintain its performance, it is more preferable that the surface of the wiping member itself be clean. For this purpose, a cleaning mechanism is often provided which presses the wiping member against an absorber to absorb the ink removed by wiping.
In the ink-jet recording apparatus, in general, ink suction in the ink flow passage of the recording head and wiping of the face are performed to maintain good discharge performance of the recording head for the purpose of preventing occurrence of printing troubles due to discharge failure (an ink droplet is not discharged from the nozzle for discharge operation, resulting in white stripes on the printed matter) caused by a bubble generated or mixed in the ink flow passage or liquid passage of the recording head, or printing troubles due to xe2x80x9cdot mis-alignmentxe2x80x9d (discharged ink is not ejected in the desired direction, resulting in white stripes on the printed matter) caused by wetting of the face of the recording head.
Wetting of the face of the recording head is also generated by the fact that the ink discharged from the discharge port is pulled from the discharge port by a surface tension of the ink and does not flow back to the liquid passage after ink discharge but appears on the face and stays there. When ink is discharged in the state in which ink remains on the periphery of the discharge port, the discharged ink is affected by the surface tension of the ink on the periphery of the discharge port, is not discharged in the predetermined direction, and appears as dot mis-alignment in the image on the printing material. Further, the wetting of the face become considerable with increasing ink discharge times.
Still further, a bubble in the ink flow passage or liquid passage of the recording head is formed while air dissolved in the ink repeats bubble generation and shrinkage due to the temperature of the recording head. When such a bubble is formed, a space not filled with ink is produced in the liquid passage which is to be filled with ink, and a discharge operation is not performed even if sufficient energy is applied, thus resulting in a printing trouble on the recording material. Yet further, such a bubble becomes liable to be formed with increasing ink discharge times.
For these reasons, it is strongly desirable to perform recovery operations such as suction and wiping when discharge times are increased; however, excessive suction tends to increase ink consumption. Further, the suction operation and wiping require interruption of the printing operation, which leads to a decrease in recording throughput.
The timing for performing the recovery operation can be determined at the time the count value of the number of discharged dots exceeds a predetermined value, thereby minimizing the number of recovery operation times including suction and wiping. Similarly, the number of dots is counted from which the amount of ink remaining in the ink supply source such as an ink tank can be calculated. Dot counting is achieved by counting electrical signals sent for generating heat by the discharge heater.
Uniform counting of all of the electrical signals is sufficient for a head which does not discharge both large and small dots from the same head. However, it is to be noted that the volumes of a large dot and a small dot differ when a head which can select large and small dots is used.
In general, a head discharging large dots is more liable to generate a bubble in the ink flow passage than a head discharging small dots, and is more liable to cause wetting of the face. From this fact, if the dot count is performed uniformly, and the recovery operation is controlled according to the counting, there is a fear that even when printing is made solely with small dots and thus there is almost no generation of an undesired bubble, suction is performed to dissipate the ink, resulting in an increase in running cost. Further, there is a fear that even when printing is made solely with small dots and there is almost no wetting of the face, wiping is performed, resulting in unnecessary interruption of the recording operation, that is, a decrease in recording throughput. Still further, if the dot count is performed uniformly regardless of discharge of large dots and discharge of small dots, as to the detection of ink remaining amount, because the difference in ink amount between large dots and small dots is not taken into consideration, there is a fear that the ink remaining amount is incorrectly determined to be xe2x80x9c0xe2x80x9d even if ink still remains in the ink tank.
With the aim of solving such problems, in accordance with the present invention, there is provided an ink-jet recording apparatus for making recording using an ink-jet recording head capable of discharging an ink in differing amounts from a discharge port, characterized by comprising ink discharge amount changing means for changing the ink discharge amount from an ink-jet recording head, accumulation means for accumulating data corresponding to ink discharge amount from the ink-jet recording head according to the change, and control means for performing processing for maintaining the ink discharge operation according to the accumulated data.
Further, according to the present invention, there is provided a control method of an ink-jet recording apparatus for making recording using an ink-jet recording head capable of discharging an ink in differing amounts from a discharge port, characterized by comprising an ink discharge amount changing step for changing ink discharge amount from the ink-jet recording head, an accumulation step for accumulating data corresponding to ink discharge amount from the ink-jet recording head, and a control step for performing processing for maintaining the ink discharge operation according to the accumulated data.
In the above, the processing for maintaining the discharge operation can include at least one of a recovery processing for maintaining ink performance from the ink-jet recording head, and a processing for detecting ink remaining amount of an ink supply source for the ink-jet recording head.
Here, the recovery processing can include at least one of an elimination processing for forcibly eliminating ink from the discharge port, and a cleaning processing for cleaning a surface provided with the discharge port of the ink-jet recording head.
In the processing for detecting the ink remaining amount, in the control means or step, the data corresponding to the forcibly eliminated ink amount can be taken into consideration.
The elimination processing can include a suction processing for sucking ink from the discharge port, and the cleaning processing can include a processing for wiping the surface.
In the ink discharge amount changing means or step, a change is performed to the ink-jet recording head so that at least two types of dots, large and small, can be formed on the recording medium, the accumulation means or step may comprise dot count means or step for separately counting the number of times of discharge operation for forming large dots and the number of times of discharge operation for forming small dots, respectively.
Alternatively, in the ink discharge amount changing means or step, a change is performed for the ink-jet recording head to be able to form at least two types of dots, large and small, on the recording medium, and in the accumulation means or step, data corresponding to the discharge operation for forming large dots and data corresponding to the discharge operation for forming small dots can be collectively counted.
In the above description, the ink-jet recording head can be one which has a plurality of heat generation resistors substantially differing in heat generation amount for generating thermal energy as an energy utilized for discharging the ink, or a plurality of heat generation resistors substantially same in heat generation amount, disposed corresponding to the discharge port.
In the ink discharge amount changing means or step, the change can be performed by selectively driving the plurality of heat generation resistors.
Further, the heat generation resistor can be one which generates thermal energy for making the ink to cause film boiling.
In the present specification, xe2x80x9crecordingxe2x80x9d (hereinafter in some cases referred to as xe2x80x9cprintxe2x80x9d or xe2x80x9cprintingxe2x80x9d) means not only a case for forming significant information such as a pattern or the like, but also a case for forming an image, figure, pattern or the like on various types of recording media, whether or not it is to be recognizable by humans using the visual sense, or a case for processing such media.
Further, xe2x80x9crecording mediumxe2x80x9d means not only paper used for a general recording apparatus, but also cloth, plastic film, a metal plate or the like and one which can accept ink discharged by the head.
Still further, xe2x80x9cinkxe2x80x9d is to be broadly interpreted as in the definition of the above xe2x80x9crecordingxe2x80x9d, and means a liquid which is applied onto the recording medium for forming an image, figure, pattern or the like, or for processing the recording medium.
As described above, according to the present invention, in the ink-jet recording apparatus for recording using an ink-jet recording head capable of discharging ink in varied amounts, processing for maintaining the ink discharge operation, for example, elimination processing for forcibly eliminating ink from the discharge port or recovery processing such as cleaning processing for cleaning the surface on which the discharge port of the ink-jet recording head is provided, or processing for detecting the ink remaining amount of the ink supply source for the ink-jet recording head or the like can be appropriately carried out.
That is, ink dissipation due to excessive ink elimination such as suction can be prevented, and the present invention is very advantageous in terms of ink consumption, thus reducing the running cost. Further, since unnecessary time consumption for suction operation or cleaning operation such as wiping can be prevented, recording throughput is not decreased, and the present invention is advantageous in terms of durability of the recording head and wiping member. Still further, since exact ink remaining amount detection can be performed, the present invention is advantageous also in view of user interface.